Though it may be required to form a skein in a filament for any of a variety of reasons, most commonly it is desirable when starting or terminating the winding a coil from wire of relatively fine gauge, or when providing a tapping part-way through a coil-winding operation. Such skeining is necessary because relatively fine wire has a very low strength and a single strand of fine copper is likely to fracture when subjected to the flexing and soldering operations necessary to terminate the coil or to provide a tapping.
Conventionally, a skein has been formed manually, by an operator folding a continuous length of the wire successively to provide several strands side-by-side and then twisting the strands axially, by rolling them between the fingers. This however requires considerable manual dexterity, and even with a skilled and experienced operator wire breakages can still easily occur. Moreover, such a manual operation makes the winding of a coil labour-intensive, and hence expensive.
In view of the disadvantages of forming skeins manually, there have been certain proposals for automatic skeining apparatus, and to some extent practical embodiments of these have helped to reduce the cost of coil-winding. A typical example of such an apparatus is shown in U.K. Patent Applications GB 2049748A and 2093382A. These machines have a flying shuttle with an eyelet through which the wire is threaded and when a skein is to be formed, the eyelet carries the wire round two spaced pins. One pin is then rotated with respect to the other, twisting the loops formed around the pins into a skein. Rather than rotating one of the pins about which the wire is looped, the loops once formed may be twisted by a twisting unit which engages the loops between the pins as shown in U.S. Pat. Nos. 4,129,158 and 4,207,927. The accurate guiding of the shuttle has caused considerable problems, especially when very fine wire is being skeined--such as copper monofilaments of a diameter as small as 0.025 mm (0.001 in)--and rapid rates of wear and high strains can occur when the apparatus is operated relatively quickly. Moreover, in view of the capital cost and size of the known skeiners of this type, it is usual to construct them so as to be suitable for the simultaneous skeining of two filaments running side-by-side. However, because a breakage of one filament almost always results in the second filament breaking, it is then necessary to run the skeiner even yet slower, so as to reduce the likelihood of a breakage even more. In addition, to reduce the probability of a malfunction of the shuttle, it has been necessary to provide complex and highly accurate mechanisms to ensure the wire is carried round the pins safely without breakages, but in turn this both decreases the reliability of the apparatus and increases the capital cost thereof.